Sunday, January 20, 2013

Dumbing Down Ventilator Taxonomy

In a recent letter to the editor “Ventilatory modes. What’s in a name?”[1] Authors provide a strong argument for the need to standardize terminology in regards to mechanical ventilation and propose an oversimplified classification system specifically for non-invasive ventilatory devices. I applaud the authors for their call to action; conversely their viewpoint is neither novel nor applicable to ventilator taxonomy.

For greater than two decades, Robert Chatburn has invested tremendously in the creation, refinement, education, promotion, and defense of a standardized taxonomy for mechanical ventilation [2-9].  Chatburn’s current classification system [1, 10] addresses the concerns that Dr. Rabec and colleagues present, which can be easily applied to non-invasive ventilation (NIV). Establishing a new oversimplified classification system specifically for NIV, I believe would further exacerbate the confusion.

The classification system proposed by Rabec et al reduces to three over-simplified characteristics (control variable, trigger variable, and cycle variable). These are necessary, but not sufficient, characteristics from which to construct a useful classification system. Attempting to use them to sort out modes ultimately frustrates the device operator.
I have three main arguments why such over-simplification does not work in regards to mechanical ventilation terminology.

First, Complexity has already been engineered into the product/device.

The level of sophistication of ventilator mode taxonomy is dependent on the intricacy of the device itself. For example a NIV device with “Adaptive Servo Ventilation” is far more intricate than a “Downs Regulator” used for Continuous Positive Airway Pressure (CPAP).  Both may provide CPAP therapy, conversely they are not equal in classification. One can merely reduce the terminology, yet this does not change the complexity of the device and thus leaves a gap in understanding.

Second, the additional classification schemes foreshadow unfortunate events.

Rabec et al justify their argument by emphasizing that there are no regulations for medical manufactures in regards to ventilator terminology and mention that new modes of ventilation are created with little changes to the previous mode. I believe this does support the need for standardization, however negates their proposal for oversimplification. Only by including the additional classification details (eg, targeting scheme and operational algorithms) one can truly identify if a new mode provides any benefit or is merely a marketing scheme. 

Additionally, once one is proficient utilizing the taxonomy proposed by Chatburn, the operator can apply this knowledge to unfamiliar modes and predict ventilator interactions to changes in pulmonary mechanics and/or changes in patient inspiratory demand.

An example of this can be demonstrated with the ventilator manufacture, marketing, and operator use of a mode which has been informally referred to as “Adaptive Pressure Control”, or APC [11]. APC has been available as a ventilator mode for greater than twenty years. This mode is characterized by a more advanced “adaptive targeting system” as compared to earlier “set-point” targeting systems [8]. However, it has been marketed as “the best of both worlds” in which the operator can target a preset tidal volume (similar to volume control ventilation) and the patient is available to receive high inspiratory flow rates if needed (because the within-breath control variable is pressure, not volume).

 In 2007 Jaecklin demonstrated that APC in a variety of ventilators regularly delivered excessive tidal volume in response to sudden increases in patient compliance or decreases in resistance potentially putting neonates at risk for lung injury [12]. Thus deflating manufacturers advertised persuasive claims of precise volume-targeting.

Within recent years in the United States, anesthesia delivery system manufacturers have made APC available on their newer generation anesthesia machines. The mode has been highly marketed for surgical procedures in which patient positioning or insufflation of the abdomen creates dramatic changes in pulmonary mechanics (e.g. laparoscopic, thoroscopic, prostatectomy, and bariatric procedures).

 Armed with prior knowledge of the operational algorithm of APC and knowing the issues in regards to tidal volume consistency during dramatic changes in pulmonary mechanics, the operator can easily predict what will happen during these surgical procedures. The abstract “Adaptive Pressure Control: tidal volume variance during simulated bariatric laparoscopic surgery” verified the inconsistency in tidal volume delivery and latency of tidal volume adaptation during inflation and deflation of pneumoperitoneum [13].

Third, oversimplification infers a notion that anyone can operate/manage a ventilatory device

In their proposal, Rabec et al support their argument by stating that application of NIV has been generalized and is carried out by non-specialized healthcare providers. I suggest that simply reducing the complexity of ventilator terminology may imply that the device is easy to use. The taxonomy suggested by Chatburn divulges specific intricacies which the operator may not understand or even be aware of. If the operator cannot apprehend these specifics related to ventilator breath delivery, then one should not attempt to use the mode in question. I would reinforce that mechanical ventilation should not be managed or applied by non-specialized health care practitioners.

I too share the goal “to make NIV management easier in clinical practice” however dumbing down ventilator taxonomy will not contribute to this objective.

1.      Rabec C, Langevin B, Rodenstein D, Perrin C, Leger P, Pepin JL, Janssens JP, Gonzalez-Bermejo J. Ventilatory modes. What’s in a name? Respir Care 2012; 57 (12): 2138-2150.
2.      Chatburn RL. A new system for understanding mechanical ventilators. Respir Care 1991; 36 (10): 1123-1155.
3.      Chatburn RL. Classification of mechanical ventilators. Respir Care 1992; 37 (9): 1009-1025.
4.      Branson RD, Chatburn RL. Technical description and classification of modes of ventilator operation. Respir Care 1992; 37 (9): 1026-1044.
5.      Chatburn RL, Primiano FP Jr. A new system for understanding modes of mechanical ventilation. Respir Care 2001; 46 (6): 604-621.
6.      Chatburn RL. Computer control of mechanical ventilation. Respir Care 2004; 49 (5): 507-517.
7.      Chatburn RL. Classification of ventilator modes: Update and Proposal for Implementation. Respir Care 2007; 52 (3): 301-323.
8.      Chatburn RL, Mireles-Cabodevila E. Closed-loop control of mechanical Ventilation: description and classification of targeting schemes. Respir Care 2011; 56 (1): 85-102.
9.      Chatburn RL, Volsko TA, Hazy J, Harris LN, Sanders S. Determining the basis for a taxonomy of mechanical ventilation. Respir Care 2012; 57 (4): 514-524.
10.  Chatburn RL. Classification of mechanical ventilators and modes of ventilation. In: Tobin MJ, ed. Principles and practice of mechanical ventilation, 3rd edition. New York:  McGraw-Hill, 2012.
11.  Branson RD, Chatburn RL. Should adaptive pressure control modes be utilized for virtually all patients receiving mechanical ventilation? Respir Care 2007, 52(4):478-488.
12.  Jaecklin T, Morel DR, Rimensberger PC. Volume-targeted modes of modern neonatal ventilators: how stable is the delivered tidal volume? Intensive care medicine 2007; 33 (2): 326-335.
13.  Richey K. Adaptive Pressure Control: tidal volume variance during simulated bariatric laparoscopic surgery. American Society of Anesthesiologists 2009. Abstract presented at the annual meeting of American Society of Anesthesiologists.